Vacuum pump



'April 6, 1948. M; MATRlcN 2,439,258

VACUUM PUMP Filed DSC. 19, 1946 l T2] .2. Z6 /9 223 ZZ /a 4 y MarcelMclT'rco, 2 29 His Al'orneg.

Patented Apr. 6, 1948 VACUUM PUMP Marcel Matricon, Paris, France,assignor to General Electric Company, a corporation of New YorkApplication December 19, 1946, serial No. 717,274 In France December 5,1942 Section 1, Public Law 690, August 8, 1946 Patent expires December5, 1962 4 Claims. (Cl. 230-205) The present invention relates toimprovements in vacuum pumps such as those of the rotary blade type.

It is known that the performance of pumps of this type involves certainfeatures which could advantageously be improved and among which may becited particularly the following:

Improved adjustment of the exhaust valve to minimize its open timethereby to obtain a higher degree of vacuum;

Improvement of irregularities in the operation of the valve during thestarting period of the pump and during the time necessary for attainingthe steady-state temperature of the oil (these two factors tend toincrease the time required to evacuate a given volume);

Improved stability in the limit vacuum which is obtained;

Minimization of noise caused by the valve;

Minimization of back-rising of the oil, when the pump is not operatinginto the, space to be evacuated.

A principal object of the present invention ls to provide a vacuumpumpimproved inA the above respects and capable of producing a higherdegree of vacuum and having various important advantages, to wit:

Improved lubrication and cooling oi the pump l body and The possibilityof introducing into the pump, oil which has been particularly treated,permitting the attainment of a very high degree of vacuum.

The present invention is especially characterized by means which duringpump operation permits the cyclic admission into the interior of thepump body of a considerable quantity of oil which may either come fromthe tank in which the pump is immersed or from another reservoir inwhich the oil is freed from gases. It is also characterized by the factthat the exhaust valve rests elastically on its seat, the latterconsisting preferably of a non-metallic material, such as a materialhaving a textile base impregnated with a Bakelite or the like.

The invention will best be understood by referring to the followingdescription and to the accompanying drawing in which Fig. 1 representsschematically a conventional vacuum pump, for example a two-blade pump;Fig. 2 is a horizontal section through the bearing of a pump embodyingthe invention: Fig. 3 is a section through Fig. 2 along the line :ir-y;Fig. 4 represents an exhaust employed with the present invention;

2 while Figs. 5 and 6 represent a modification of the embodiment ofFigs. 2 and 3.

The preferably cylindrical closed pump chamber I in Fig. 1 is immersedin tank 2 lled with oil 3 and covered by lid 4. The pump chamber I hasan inlet port 5 through which the pump interior may communicate with thereceptacle which is to be evacuated by means of an appropriate pipe 6.An exhaust valve 1 positioned in the outlet port permits communicationbetween the inside of the pump and the outside. This exhaust valve vmaycomprise a ball 8, which is forced against its seat by its own weight orthrough a spring arrangement 9 which can be adjusted so as to preventtoo high a pressure against the exhaust end.

Within the pump chamber, a cylindrical rotor I 0 rotatable about itsaxis rests tangentiallyagainst the wall of the pump chamber I at pointII. The rotor may comprise two resiliently mounted blades I2 and I3which are forced against the inside walls of the pump chamber by aspring I4. The rotor and the blades rotate in a direction indicated bythe arrow.

In Figs. 2 and 3, a pump embodying the invention is shown as comprisinga cylinder I5 closed at its ends by end plates I8 and I1. A cylindricalrotor I8 journaled in bearings I9 and 20 in end plates I3 and I'lrespectively, is mounted for rotation about its axis in close tangentialcontact with the inner wall of cylinder I5. Rotation in the directionindicated by the arrow may be effected by any suitable means such as apower source (not shown) applied to shaft 2|.

A duct or canal 22 is drilled into plate I6 through which ductcommunication is established between the outside and a radial duct 23within the hub or journal 24 of the rotor I8. In duct 23, a closelyttingball 25 is placed. Said duct 23 communicates also with duct 26terminating within the pump cylinder I5. Duct 22 may be connected to theoil 3 (Fig. 1l of tank 2 or to a tank filled with specially treated oil.To simplify the figure, the duct 26 is shown diametrically opposite'duct 22. However, this duct 2B could be at any angle with respect toduct 22. Rotor I8 is provided with blades 21 and 28, and spring 29 allhaving the same function as their counterparts in Fig. 1.

Pumps embodying the present invention may also comprise pipe 30connecting the inside of cylinder I5 to the receptacle to be evacuatedand an exhaust valve 3l similar to those in Fig. 1. Fig.' 4 shows ingreater detail a suitable exhaust valve comprising valve head 32subjected to the pressure of a relatively powerful spring 33 landresting against the resilient seat 34 which consists of a material .thatwill prevent noise during the pump operation. This material may be anysuitable material such as textile impregnated with Bakelite.

These various arrangements operate as follows:

During the rotation of the rotor I8, the inside of the pump cylinder Iis evacuated, so that oil may be drawn through duct 22 tolfill the duct23 of hub or journal 24 when one of its openings is aligned with duct22. One half revolution of rotor I8 later, the quantity of oil is drawnthrough the duct 26 and penetrates into the `pump cylinder. The processis repeated cyclically. The admitted oil is expelled when the blades 21and 28traverse the cylinder and is compressed into the dead space, i.e., the space between the Valve seat and the blades which would normallycontain small pockets ofl .air not completely expressed from the pump.The oil then lifts the valve 3| to evacuate the trapped air and acertain amount of the oil itself.

When one of the blades passes in front of the suction port from pipe 30,it separates a certain volume of air V at the pressure P. If v is thedead space, and if V kw is the compression ratio, the limit pressurewhich the pumps can attain will be where H is the external pressure towhichy the valve is subjected, a pressure whichisalmost equal toatmospheric pressure.

It will be seen that by considerably decreasing the effect of the deadspace by filling it with an appreciable quantity of oil, one can obtainvery low limit pressures and by use of the present invention there maybe admitted to the cylinder during each revolution a quantity of oilwhich is just necessary to make the dead space practically zero.

Pumps constructed in accordance with the present invention operate veryevenly in the cold as well as in the hot state, since the quantity ofoil admitted is constant and does not depend on the exhaust valvepressure or on the viscosity of the oil.

The advantages oered by pumps constructed in accordance with theinvention become Very apparent when one considers the conventional pumpsin which only a very slight quantity of oil is introduced into the pumpcylinder in order to insure the lubrication of the frictional surfaces.This slight admission of oil takes place, to a slight extent, by way ofthe leakage paths along the bearings or flanges, and especiallythroughthe entrance of oil during the downward stroke of the exhaust valve.Adjustment of the latter, limiting the time during -which it is open,permits a variation in the quantity ofoil admitted; however, if thevalve is left open for too long a time, the air and oil which had beenpreviously expelled by the blade re-enter the pump cylinder after theblade has passed. In the latter event the problem of air evacuation isconnected to that of oil admission. By means of the present inventionthese two factors are made completely independent of each other.

Another advantage of the present invention lies in the fact that the oiladmitted to the vacuum chamber of the pump may be one which does notcontain air bubbles since this oil may be drawn from a tank at a pointremote from the exhaust or may be taken from a container in which theoil is especially treated to degas it. Thereby one may take advantage ofthe great avidity with which degassed oil may absorb air. In this way amuch better vacuum is attained.

Finally, the relatively powerful spring 33 (Fig. 4) lsuppresses therising of oil, owing to the high pressure with which it rests againstvalve head 32 and forces the latter on its seat 34, quite in con- Atrast tothe light spring 9, which was used formerly, as was shown inFig. 1.

In Figs. 5 and 6 there is shown a variant form in which the duct 23consists simply of a single ended hole without ball and which operateson the same principle as that already described. In all other respectsthe construction of Figs. 5 and 6 is the same as that of Figs. 2 and 3,and like numerals have been used to designate like parts.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that variouschanges and modications may be made Without departing from the inventionin its broader aspects and, therefore, it is the aim of the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: n

1. A pump for gaseous fluids comprising a closed cylindrical pumpchamber including a cylindrical wall and end plates constituting endWalls, inlet and outlet ports positioned at diierent points on theperiphery of said cylindrical wall, a cylindrical rotor of diameter lessthan that of said cylindrical wall tangentially engaging the saidcylindrical wall between said ports and having a journal in one of saidend plates, resilient blades on said rotor for pumping gaseous uid fromsaid inlet to said outlet port, and means within said journal and saidone of said end plates for cyclicly injecting a quantity of oil intosaid chamber, said last mentioned means comprising a first duct withinsaid one of said end plates having an externally accessible opening andterminating in an opening juxtaposed to said journal, a second ducthaving an opening into said chamber and terminating in an openingjuxtaposed to said journal, and a duct within said journal alignablewith said first and second ducts at predetermined angular positions ofsaid rotor.

2. A pump for gaseous uids comprising a closed cylindrical pump chamberincluding a cy-v lindrical wall and end plates constituting end' walls,inlet and outlet ports positioned at diiferthe emulsion of air and oiladmittedinto the pump impairs the Vacuum and limits the degree of vacuumwhich can be obtained. ,It isfor this reason that only a slightre-entrance of pil, hasv been allowed into these pumps heretofore,`since ent points on the periphery of said cylindricalV wall, acylindrical rotor of diameter less than that of said cylindrical walltangentially engaging the said cylindrical wall between said ports andhaving a journal in one of said end plates,

prising a irst duct within said one of said end plates having anexternally accessible opening and terminating in an opening juxtaposedto said journal, a second duct having an opening into said chamber andterminating in an opening juxtaposed to said journal, and a duct withinsaid journal alignable With said first and second ducts at predeterminedangular positions of said rotor, and means within said duct within saidjournal for interrupting continuous ilow of oil through said ducts.

3. A pump as in claim 2 in which said last mentioned means comprises aflow blocking member having a cross section conforming substantially tothat of said duct within said journal and moveable from one end thereofto the other whereby said duct may receive a charge of oil when alignedwith said rst duct and may deliver said charge to said chamber whenaligned with said second duct.

4. A pump'as in claim 2 in which said last mentioned means comprises anend wall closing one end of said duct Within said journal whereby saidduct may receive a charge of oil when aligned with said first duct andmay deliver said charge to said chamber when aligned with said secondduct.

MARCEL MATRICON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 848,446 Crowell Mar. 26, 19071,675,686 Barnes July 3, 1928 2,018,341 Badger Oct. 22, 1935 2,050,533Huff Aug. 11, 1936 20 2,393,690 Johnson Jan. 29, 1946

